## Iteration 23 — Phase 8 (close)

Closes 2026-05-14. iter23 = kernel printk inside `v4l2_ctrl_request_setup` outer loop, BEFORE the `continue` check, logging every iteration. FULL close.

### Method

`linux-fresnel-fourier 7.0-7` added one pr_info at TOP of the outer loop in `v4l2_ctrl_request_setup`, BEFORE `if (ref->req_done || (ctrl->flags & V4L2_CTRL_FLAG_READ_ONLY)) continue;`:

```c
pr_info("iter23_loop: id=0x%x req_done=%d flags=0x%x ncontrols=%d cluster0_id=0x%x\n",
    ctrl->id, ref->req_done, ctrl->flags,
    master->ncontrols,
    master->cluster[0] ? master->cluster[0]->id : 0);
```

### Result — definitive

**libva HEVC** (first setup): iter23_loop fires for 16 IDs ending at 0xa40a90 (HEVC_SPS). **The outer loop EXITS before reaching 0xa40a91.**

**kdirect HEVC** (first setup): iter23_loop fires for 22 IDs ending at 0xa40a96 (HEVC_START_CODE). **The outer loop completes normally.**

The loop body has only two exit-loop paths after the iter23_loop printk fires:
1. `goto error` if `req_to_new(r)` returns non-zero.
2. `break` if `try_or_set_cluster(NULL, master, true, 0)` returns non-zero.

For libva, ONE of these fires AT HEVC_SPS, exiting the loop. For kdirect, NEITHER fires.

This **fully overturns iter21/22**:
- The clone-hdl IS complete for libva (iter22 confirmed all 22 controls cloned).
- The setup loop reaches HEVC_SPS for libva (iter23 confirmed).
- The processing of HEVC_SPS in the setup loop FAILS for libva.

The failure of HEVC_SPS processing means:
- `p_cur` for HEVC_SPS is never committed → rkvdec reads zero (iter20 finding).
- All subsequent compound HEVC controls (PPS, SLICE_PARAMS, SCALING_MATRIX, DECODE_PARAMS, DECODE_MODE, START_CODE) NEVER reach their processing → their `req_done` stays false but they're also never committed → all zero in `ctx->ctrl_hdl`.

### Why does HEVC_SPS processing fail for libva but not kdirect?

The most likely candidates:

| Function | Failure modes |
|---|---|
| `req_to_new(ref_SPS)` | -ENOENT if `!p_req_valid`. -EINVAL if elem count mismatch (`p_req_elems != p_array_alloc_elems` for non-dyn-array). -ENOMEM if alloc fails for dyn-array resize. |
| `try_or_set_cluster(NULL, master_SPS, true, 0)` | Validator failures (out-of-range field values). Cluster ops failures. Often returns -EINVAL or -ERANGE. |

iter24 will pinpoint which function fails and what return value.

### iter21/22's interpretation errors

- **iter21**: I concluded the clone-hdl was missing controls. Wrong — the iter21_setup_ref printk was inside the loop body but AFTER the early-continue check. The "missing" controls were actually iterated past after SPS's processing failed and the loop exited — they never even saw the iter21 printk.
- **iter22**: The clone trace confirmed clone-hdl is complete. Good. But my mid-conclusion ("clone-hdl is complete; staging fails in setup loop SKIP path") was partially wrong — the loop doesn't SKIP, it EXITS.

### Mechanism status (post-iter23)

| # | Mechanism | Status |
|---|---|---|
| 1 | request_fd mismatch | DISPROVED iter17/18 |
| 2 | REINIT clears | DISPROVED iter19 |
| 3 | Stack-locals stale | DISPROVED iter18 |
| 4 | ctrl_hdl mismatch | DISPROVED iter20-22 |
| 5 | error_idx silent failure | DISPROVED iter18 |
| 6 | req->p_new staging incomplete | DISPROVED iter22 |
| 7 | Clone-hdl missing controls | DISPROVED iter22 |
| 8 | Skip-loop bypass | DISPROVED iter23 (loop EXITS, not skips) |
| 9 | **NEW iter23**: HEVC_SPS processing in v4l2_ctrl_request_setup fails for libva | **LEADING — iter24 candidate** |

### iter24 candidate

`linux-fresnel-fourier 7.0-8`:

```c
ret = req_to_new(r);
pr_info("iter24_req_to_new: id=0x%x ret=%d p_req_valid=%d p_req_elems=%u\n",
    master->cluster[i]->id, ret, r->p_req_valid, r->p_req_elems);
...
ret = try_or_set_cluster(NULL, master, true, 0);
pr_info("iter24_try_or_set: master_id=0x%x ret=%d\n", master->id, ret);
```

After 7.0-8 deploys, libva HEVC will show:
- `iter24_req_to_new id=0xa40a90 ret=X p_req_valid=Y p_req_elems=Z` where X is the actual return value.
- If req_to_new ret != 0 → bug is in req_to_new for HEVC_SPS on libva's staged data. Compare p_req_elems to kdirect's value.
- If req_to_new ret == 0 → check iter24_try_or_set's ret. If non-zero → validator rejects libva's SPS but accepts kdirect's. Investigate which field validator rejects.

### Substrate state at iter23 close

- Backend SHA on fresnel: `c1d4bb53…` (iter15 stable, unchanged).
- Fork tip `e109306` — unchanged.
- Kernel `linux-fresnel-fourier 7.0-7` with iter17 + iter20 + iter21 + iter22 + iter23 printks.
- 5-codec anchors: unchanged.

### iter24 build kicked off

`linux-fresnel-fourier 7.0-8` building on boltzmann (PID 1672261, log /tmp/iter24-kbuild.log).

### Lesson

Three iterations of mid-loop printk (iter21, iter22, iter23) needed to localize the exit. Each iteration overturned the previous's partial conclusion. Key methodology: **place the diagnostic printk at the very top of each loop body, BEFORE any continue/break, to distinguish "skipped" from "exited"**. Without that, "missing from printk output" is ambiguous.

The bug is now localized to:
- A specific function: `req_to_new` OR `try_or_set_cluster`.
- A specific control: HEVC_SPS.
- A specific request lifecycle pattern: libva's, not kdirect's.

One more printk iteration (iter24) should give the failing function + return code.
